Proper prediction of Length Of Stay (LOS) has become increasingly important these years. The LOS prediction provides better services, managing hospital resources and controls their costs. In this paper, we implemented and compared two Machine Learning (ML) methods, the Random Forest (RF) and the Gradient Boosting model (GB), using an open source available dataset. This data are been firstly preprocessed by combining data transformation, data standardization and data codification. Then, the RF and the GB were carried out, with a phase of hyper parameters tuning until setting optimal coefficients. Finally, the Mean Square Error (MAE), the R-squared (R2) and the Adjusted R-squared (Adjusted R2) metrics are selected to evaluate model with parameters.